Form-based authentication allows the developer to control the look and feel of the login authentication screens by customizing the login screen and error pages that an HTTP browser presents to the end user. When form-based authentication is declared, the following actions occur:
A client requests access to a protected resource.
If the client is unauthenticated, the server redirects the client to a login page.
The client submits the login form to the server.
The server attempts to authenticate the user.
If authentication succeeds, the authenticated user’s principal is checked to ensure it is in a role that is authorized to access the resource. If the user is authorized, the server redirects the client to the resource using the stored URL path.
If authentication fails, the client is forwarded or redirected to an error page.
Figure 25–3 shows what happens when you specify form-based authentication.
The following example shows how to declare form-based authentication in your deployment descriptor:
<login-config> <auth-method>FORM</auth-method> <realm-name>file</realm-name> <form-login-config> <form-login-page>/logon.jsp</form-login-page> <form-error-page>/logonError.jsp</form-error-page> </form-login-config> </login-config>
The login and error page locations are specified relative to the location of the deployment descriptor. Examples of login and error pages are shown in Creating the Login Form and the Error Page.
Form-based authentication is not particularly secure. In form-based authentication, the content of the user dialog box is sent as plain text, and the target server is not authenticated. This form of authentication can expose your user names and passwords unless all connections are over SSL. If someone can intercept the transmission, the user name and password information can easily be decoded. However, when a secure transport mechanism, such as SSL, or security at the network level, such as the IPSEC protocol or VPN strategies, is used in conjunction with form-based authentication, some of these concerns can be alleviated. To add a protected transport in your application, use the elements described in Specifying a Secure Connection.
The section Example: Form-Based Authentication with a Servlet is an example application that uses form-based authentication.
When creating a form-based login, be sure to maintain sessions using cookies or SSL session information.
As shown in Form-Based Authentication, for authentication to proceed appropriately, the action of the login form must always be j_security_check. This restriction is made so that the login form will work no matter which resource it is for, and to avoid requiring the server to specify the action field of the outbound form. The following code snippet shows how the form should be coded into the HTML page:
<form method="POST" action="j_security_check"> <input type="text" name="j_username"> <input type="password" name="j_password"> </form>